Imovie 09 on mac wont respond?

I recently bought an imac, and had been using imovie 09 with no problems. However one day I imported a .mov file. It became very laggy, and now every time I open imovie all I can see if a ring spinning. I read on a forum that if i deleted the com.apple.iMovie.plst it may work. I did this but all that changed was the optimizing movie loading bar came up followed by it closing. I made a new account and tried it on that and it worked fine but i need to have it on this account.